A Coplanar-Strip-Based Excitation Technique for Wide 3-dB Axial Ratio Beamwidth and Enhanced Circular Polarization Antenna

This paper presents a new feeding technique for excitation of circular polarization (CP) in a planar wide-slot antenna with enhanced axial ratio (AR) bandwidth and wide 3 dB AR beamwidth. To achieve a wide 3 dB AR beamwidth, two parasitic L-shape strips are positioned coplanar to the microstrip line extension of an asymmetrical coplanar waveguide (CPW). For additional CP modes, a horizontal strip is protruded from the vertical edge of the ground plane towards the center of the slot etched in the ground plane. With this technique, not only the 3 dB AR beamwidth is improved but also a wide AR bandwidth is obtained. The total footprint of the antenna realized using the outlined approach is Ls × Ws = 0.3 λ0 × 0.28 λ0 with λ0 being the free space wavelength at the lowest operating frequency of the antenna. Additionally, a wide impedance bandwidth of up to 72-percent (2.26 GHz-4.85 GHz) is achieved along with the AR bandwidth of 66% (2.44 GHz- 4.87 GHz). Furthermore, for the 58-percent of the total AR bandwidth a wide 3 dB beamwidth of 85° ± 5° is maintained without involving any complex circuitry. Finally, the antenna features realized gain of 3.7 dBi (averaged over the entire operating band).